Television replays showed Marler, playing his first match since serving a suspension for calling Wales' Samson Lee "gypsy boy" during last month's Six Nations, appeared to kick Heguy as the Frenchman lay on the ground during Harlequins' 30-6 victory.
The referee missed the incident but Marler could yet be punished if the citing commissioner decides he should face a disciplinary hearing.
Harlequins director of rugby Conor O'Shea said the incident was not worthy of a red card.
"Any test for a citing has to pass the red-card test," said O'Shea. "Should he do it? No. Is it a red card? No."
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A lengthy ban could rule Marler out of England’s tour of Australia in June.
(Reporting by Toby Davis; editing by Peter Rutherford)
